1. Field of the Invention
The present invention relates to a transmission system comprising a transmitter having, signal combining means for combining a first and a second signal forming a combined signal and having transmission means for transmitting the combined signal. Such a transmission system can be a broadcasting system for broadcasting stereo signals to receivers, or a system for recording and reproducing stereophonic signals, or any other system for combined signals.
The present invention further relates to a transmitter for use in such a system.
The present invention further relates to a receiver for use in such a system.
2. Description of the Related Art
A transmission system of this kind is known from "Electronics Engineer's Reference Book", L. W. Turner, London, Newnes-Butterworths, 1976, pp. 15-56 to 59, and pp. 15-166 to 170. In this handbook, a well-known stereophonic system is described, in which first and second stereophonic audio signals, the so-called left and right stereo channels, are combined forming a stereophonic transmission signal for broadcasting to receivers. First, a summing signal is formed from the first and the second signal, and further, with the help of a balanced modulator and a sub-carrier at a double frequency of a so-called pilot tone, a difference signal is built. Then, a combined signal, formed from the summing signal, the difference signal, and the pilot tone, is modulated onto a carrier and is transmitted to the receivers. In the receivers, after demodulation, the summing and the difference signals are separated from the pilot tone, and the first and second signals are extracted from the summing and difference signals by respective summing and subtraction of the same by means of a stereo decoder. Such a stereo transmission system is complicated as regards coding and decoding of the left and right stereo signals. Besides, the phase relationship between the pilot tone frequency and the sub-carrier is very critical. Also, such a system requires relatively complicated and time consuming adjustment procedures.